In recent years, for the purpose of enlarging the use of an organic electroluminescence device (sometimes referred to as “organic EL device” in this specification), the development of materials towards not only improvements of luminous efficiency and durability of the device but also full-color display, realization of a large area and mass production is actively carried out.
In order to realize full-color display, it is necessary to use materials capable of emitting monochromatic light of each of red, green and blue colors which are primaries (RGB). However, there was encountered a problem that any organic material capable of highly efficiently emitting red light with a high luminance brightness is not obtained.
Patent Document 1 discloses an iridium complex which is constituted of iridium and a quinoline derivative as a material capable of emitting red to orange light. According to Patent Document 1, an organic EL device is prepared by dispersing this iridium complex in a host material and forming a film by a vacuum vapor deposition method to obtain a light emitting layer.
However, the vacuum vapor deposition method involves a problem that not only a vacuum unit is required, but also in the case of a large-area device, the film thickness is liable to become non-uniform.
For that reason, if a light emitting layer could be formed by coating a solution of a light emitting material containing an organic solvent or water, not only the manufacturing step of an organic EL device is made simple, but also it is possible to realize a device with a large area. In this coating method, since a small light-emitting molecule which is liable to cause phase separation or segregation, there is made an attempt to obtain a light emitting polymer material which is free from such defects.
Also, for the purpose of efficiently causing recombination of a hole and an electron on a light emitting compound, thereby designing to improve luminous efficiency, there is also made an attempt to obtain a light emitting polymer material resulting from copolymerization of a light emitting compound and a hole transport compound and/or an electron transport compound.
For example, an organic EL device is prepared by using, as the light emitting polymer material, a copolymer comprising a structural unit derived from an iridium complex, a carbazole derivative, and an oxadiazole derivative. In such an device, in the case where an iridium complex having a phenylpyridine derivative coordinated therein is used, green light emission is observed (see Patent Document 2); and in the case where an iridium complex in which an acetylacetone derivative bound to the polymer main chain and a quinoline derivative are coordinated is used, red light emission is observed (see Patent Document 3).
However, for the purpose of achieving practical application of light emitting polymer materials, it has been desired to develop a durable light emitting polymer material which is able to highly efficiently emit red light with a high luminance brightness and to simplify the manufacturing step of an organic EL device.
[Patent Document 1] WO 2002/064700
[Patent Document 2] JP-A-2003-342325
[Patent Document 3] JP-A-2004-27088